DISTINCT MECHANISMS REGULATE INDUCTION OF MESSENGER-RIBONUCLEIC-ACID FOR PROSTAGLANDIN (PG) G H SYNTHASE-2, PGE (EP(3)) RECEPTOR, AND PGF(2-ALPHA) RECEPTOR IN BOVINE PREOVULATORY FOLLICLES/

We have evaluated the in vivo and in vitro regulation and temporal exp ression of messenger RNA (mRNA) for prostaglandin (PG) G/H synthase-2 (PGHS-2) and two specific PG receptors, PGF(2 alpha) receptor (FP rece ptor) and PGE receptor EP(3) subtype (EP(3) receptor), in bovine preov ulatory follicular cells and luteal cells. An in vivo study showed tha t PGHS-2 mRNA was not detected in granulosa cells and was highly but t ransiently induced by the LH surge before ovulation. FP and EP(3) rece ptor mRNAs were present at extremely low concentrations in granulosa o r thecal cells and did not increase before ovulation. Messenger RNA fo r FP receptor increased more than 500- and 2500-fold at 24 sind 48 h a fter ovulation, respectively, and these high amounts were maintained a t midluteal phase. On the other hand, mRNA for EP(3) receptor remained low with FP receptor mRNA 1000-fold greater than EP(3) receptor mRNA in the corpus luteum. In vitro culture of bovine granulosa cells using hCG, forskolin, and phorbol didecanoate demonstrated that induction o f FP receptor mRNA was mediated through protein kinase (PK) A. In cont rast, EP(3) receptor mRNA was stimulated through PKC. PGHS-2 was acute ly (<12 h) increased by PKA, and to a lesser extent by PKC. Temporal e xpression of FP receptor mRNA is not consistent with the involvement o f FP receptor in ovulation and suggests that PKA stimulates PGHS-2 and FP receptor mRNA by distinct mechanisms.